This research will investigate genetic and dietary influences on the Phase I metabolism of tobacco smoke carcinogens and on lung cancer risk. Based on recent findings, we hypothesize that, in smokers: 1) polycyclic aromatic hydrocarbons (PAHs) in tobacco smoke are the primary cause of squamous cell carcinoma of the lung, whereas nitrosamines in tobacco are the primary cause of lung adenocarcinoma; 2) the metabolic activation of PAHs is mainly carried out by CYPIA1, with more minor roles for CYP3A4 and CYP1B 1, and the activation of tobacco-specific nitrosamines (TSNAs) is mainly carried out by CYP2E1, CYPlA2 and CYP2A6; and 3) the activation of these carcinogens is modified by polymorphic genes and dietary inhibitors/inducers. We will use genomic DNA samples from a completed case-control study of lung cancer among Japanese, Caucasians and Hawaiians (341 cases, 456 controls) to test the independent and joint associations of these polymorphisms with lung cancer risk. We will also conduct a cross-sectional study (n=600) among Japanese, Hawaiian and Caucasian smokers participating in our Multiethnic Cohort Study to test associations of: 1) urinary NNAL (the main metabolite of NNK) and TSNA globin adducts with the high activity genotypes for CYP2E1, CYIA2 and/or CYP2A6; 2) urinary total 1-hydroxypyrene and levels of PAH DNA adducts in circulating lymphocytes with the high activity genotypes for CYPIAI, AhR and CYPIBI; and 3) intake and urinary levels of phytochemicals (specific flavonoids, total isothiocyanates) and plasma levels of micronutrients with these markers of activation. Finally, two feeding studies (n=50 each) will use a randomized cross-over design to test the effect of selected foods on markers of PAH or TSNA metabolism and on metabolizing enzymes in smokers with high and low activity genotypes. The elucidation of the main enzymes responsible for carcinogen activation and of the impact of dietary factors on these enzymes would have important implications for cancer prevention.